Oscillator-modulator circuit



Oct. 17, 1933. H. A. WHEELER I 1,931,338

OSCILLATOR-MODULATOR QIRCUIT Filed Jan. 20, 1932 INVENTOR HAROLD A WHEELER ATTORNEYS E I Patented Oct. 17, 1933 PATENT oFF cs OSCILLATOR-MODULATOR CIRCUIT Harold A. Wheeler, Great Neck, N. Y., assignor to Hazeltine Corporation Application January 20, 1932. Serial No. 587,681

17 Claims.

The present invention relatesto oscillator modulators, and more particularly to an oscillator modulator for use in connection with superheterodyne radio receivers.

In a superheterodyne radio receiver it is customary to convert the desired carrier or signal frequency currents into currents of a single predetermined intermediate frequency. The intermediate frequency is usually lower than the carrier frequency to facilitate the further amplification and selection of the desired signal. This frequency-changing process has, for the best results, formerly required an oscillator and modulator or first detector, each requiring an individual tube.

Although it has been proposed to utilize a single tubefor the purpose of generating the local or heterodyne frequency currents, and combining the currents thus produced with the re- 20 ceived signal currents, it has been found that a single tube could not perform both functions efficiently because of overloading effects of the oscillations, especially in the grid circuit, partly due to the widely differing oscillation voltages obtained at the various portions of the tuning range of the oscillator. When a signal is applied from a tuned circuit to the grid of an oscillating vacuum tube, any appreciable grid current causes a damping of the tuned circuit and a distortion of the signal currents, producing also cross modulation of the desired signal by strong interfering signals.

It is the principal object of the present invention to produce an oscillator modulator arrangement in which the oscillator shall be self-regulating to permit the grid circuit of the modulator to be free from overloading grid current at any point in the tuning range without a critical adjustment of the feed-back and without relying upon -overloading or saturation effects in the plate circuit to control the amplitude of oscillation.

It is a further object of the present invention to provide an oscillator modulator circuit in which the self-regulation of the oscillator may be employed without a sacrifice of conversion gain in the modulator.

These and further objects of this invention will become apparent from the following specification taken in connection with the accompanying drawing.

For accomplishing the objects of the present invention, there is provided an oscillator modulator circuit which employs an oscillator circuit of the type shown in cop ding application for "Feed-back circuits, Serial No. 540,581, filed May 28, 1931, of which this application is a continuation in part. q

This oscillator circuit is of the uniform voltage type in which the feed-back from the2output I to the oscillation circuit includes a pair of couplings whose feed-back effects vary oppositely with frequency in order that the oscillation voltage may be maintained uniform as the tuning is varied. The feed-back from the oscillation circuit into the input circuit is so proportioned relat ve to the oscillation voltage that the maxim input voltage, due to the oscillation feedback and the maximum signal input, will be insufiicient to cause the grid to draw current and yet shall at all times be suificient to maintain oscillations. The output circuit includes a portion of the oscillation circuit, providing a direct coupling to the output circuit which varies inversely with frequency. in order to assist in promoting a uniform output for the oscillator modulator regardless of the frequency to which the oscillator is tuned.

Having thus briefly described this invention, attention is invited to the accompanying draw- 8 ing, in which:

Fig. 1 is'a diagram showing a and Fig.2 is a modified circuit diagram showing an oscillator modulator embodying the features of the present invention.

Fig. 1, to which attention is-now invited, -in-- -cludes a vacuum tube 11 of the tetrode or screen-grid type, which may be of type 224,

and a resonant frequency-determining or oscillation circuit 22 including inductance 12, a fixed condenser 13, and avariable condenser 14 in series with each other. The junction between the condensers 13 and 14 is grounded, and the junction. point between the condenser 13 and indiictance 12 is connected to the anode of the tube 11 through an inductance 15 in series with fixed condenser 16. The cathode of tube 11 is connected toground through an inductance 1'1 in series with a parallel combination of the radie-frequency by-pass condenser 18 and resistance 19, which serves the purpose of furnishing a bias voltage between the grounded grid and the cathode. The screen-grid is grounded through a battery 20. Inductances 17 and 15 are each magnetically coupled to inductance 12, as indicated by the brackets.

The anode potential for the tube is supplied. by a battery 21 in series with choke coil 51. The radio-frequency component of the anode cursimple oscillator,

tance; a feed-back coupling between saidoscillation circuit and the inputcircuit of thetube; a connection between said inductance and said anode; and an output circuit connected-between said anode and said cathode and including an output inductance, said connection, said fixed condenser, and a source of high potential energy connected between said output inductance and the junction of the two condensers of said oscillation circuit, whereby the fixed condenser of said oscillation circuit is also included in the output circuit and thus simultaneously serves to assist in tuning the output circuit to resonance with the desired frequency and in producing a capacitive coupling between the output circuit" and the oscillation circuit, which coupling will vary inversely with frequency.

4. In a superheterodyne radio receiver, an oscillator modulator circuit which includes a vacuum tube-having input and output terminals;

I an input circuit connected to said input 'terminals and including a resonant portion which istunable to the frequency of a signal; a tuned oscillation circuit inductively coupled to said in put circuit and tunable to the oscillation frequency; a tuned output circuit connected to the output terminals of said vacuum tube and coupled to said oscillation circuit, said circuit being tuned to the intermediate frequency; an intermediate-frequency circuit inductively coupled to said output circuit; and a capacitive coupling common to said oscillation circuit and said output circuit, whereby the reactance of said oscillation circuit upon said output circuit will increase with a decrease in frequency to offset decrease in transfer voltages due to the inductive coupling between the oscillation circuit and input circuit.

5. In a superheterodyne radio receiver, an oscillator modulator system which includes a vacuum tube having input-and output electrodes, input and output circuits connected to said input and output electrodes, respectively, an oscillation circuit coupled between said input and output circuits, means for tuning said output circuit to the intermediate frequency, an intermediate-frequency amplifier input circuit induc-' tively coupled to said output circuit, and reactance means, common to said oscillation and output circuits, said reactance means being of such a character that the reactance of said oscillation circuit upon'the input circuit will increase with a decrease in frequency to permit a lilntgform translation gain in said oscillator modu- -6. In a superheterodyne radio receiver, an oscillator modulator circuit which includes a vacuum tube having anode, grid, and cathode; an

input circuit connected between said cathode and said grid and including a portion which tunable to the frequency of.a signal; an oscillation circuit including a fixed condenser, a variable condenser, and an inductance in series; a connection between said inductance and said anode including a third condenser; an output inductance connected to said anode; a connection from said inductance to a Junction of the two condensers of said oscillation circuit, whereby said output inductance is tuned by the fixed condenser of said oscillation circuit andthe thirdmentioned, condenser, and whereby the capacitive coupling between said oscillation and output circuits will tend' to give a uniform translation gain to said oscillator modulator circuit.

'1. An; electric generating system which ina the output circuits of said'tube, and a fixed impedance common to said output circuit and said cludes a 'vacuum tube having input. and outputterminals, a circuit connected to the input terminals of said tube and including a tunable resonant portion, a fixed resonant circuit connected to the output terminals of said tube, a tunable oscillation circuit coupled to said input and said output circuits, and a fixed auxiliary impedance means'coupled thereto and tosaid fixed resonant circuit, whereby substantially uniform output voltage is developed by said generator.

8. An electric generating system which in-V cludes a vacuum tube having input and output terminals, input and output circuits connected to said input and output terminals, respectively, said input circuit including a portion which is tunable to a first frequency and said output circuit being tuned to a second frequency, a tunable oscillation-circuit tuned to a third frequency and inductively coupled to the input and coupled to oscillation circuit, whereby the effective coupling between said oscillation circuit and said output circuit increases with a decrease in frequency to oifset the changes caused by' the inductive feedback coupling assaid oscillation circuit is tuned through a band of frequencies.

9. An oscillator modulator'circuit comprising a vacuum tube having grid, cathode, and anode; an oscillation circuit including in series an inductance,- a fixed capacity and a variable capacity connected; a fixed coupling capacity connected between said inductance and said anode; a ground connection connected to the junction of the capacities of said oscillation circuit; an output inductance connected to said anode; and a source of high potential energy connected between said output inductance and ground whereby the fixed capacity of said oscillation circuit and the coupling capacity between said circuit and the anode of said: tube serve to tune said inductance to the outputfrequency of said os-' cillator. 10.. An electric generating system which includes a vacuum tube having input and outputv terminals, input and output circuits connected to said input and output terminals, respectively, said input circuit including a portion which is tunable to a first frequency and said output circuit being tuned to a second frequency, a tunable oscillation circuit tuned to a third frequency and coupled to 'the output and input circuits of said tube, and a fixed impedance common to said output circuit and said oscillation circuit, whereby the reactance of said circuit upon the output circuit will increase with a decrease in the frequency to which said oscillation circuit is tuned. I

11. An oscillator system, tunable over a frequency range, comprising a vacuumtube-having'135 cathode, grid, and anode; an oscillation circuit including an inductance; a fixed condenser and a condenser which is variable to tune said circuit; a condenser connected between said'inductance and said anode; and an output inductance connected to'said anode and tuned by means of said last-mentioned condenser and the fixed condenser of said oscillation circuit.

' 12. An electric generating systemwhich includes a vacuum tubehaving input and output tween said oscillation circuit and saidinput circuit being inductive, and the coupling between said output circuit and said oscillation circuit being combined capacitive and inductive, whereby the reactance of said oscillation circuit upon said output circuit will increase with a decrease in frequency to offset the decrease in transfer voltage caused by the inductive coupling be tween the oscillation circuit and the input circuit. I

. 13. An electric generating system which includes a vacuum tube having input and output terminals, input and output circuits connected to said input and output terminals, respectively, a tunable oscillation circuit coupled to both of said circuits, 2. utilization circuit inductively coupled to said output circuit, the coupling be tween said oscillation circuit and said input circuit being-inductive, and the coupling between said output circuit and said oscillation circuit being capacitively reactive, whereby the reactance of said oscillation circuit upon, said output circuit will increase with a decrease in irequencyto offset the decrease in transfer voltage caused by the inductive coupling between the oscillation circuit and the input circuit.

14. An electric generating system which includes a vacuum tube having input and output terminals,.an input circuit connected to the input terminals of said tube, an output circuit connect'ed to the output terminals of said tube, a tunable oscillation circuit coupled to said input and output circuits, and a fixed auxiliary-impedance means coupled thereto and to said output circuit, whereby substantially uniform output voltage is developed by said generator.

, oscillation frequency and feed-back and output an inductance, a fixed capaclty,'and a variable capacity; a coupling capacity connected between said inductance and said anode; an output inductance connected to said anodes and a source of high potential energy connected between said output inductance and the junction of the capacities of said oscillation circuit, whereby the fixed capacity of said oscillation circuit and the coupling capacity between said circuit and the anode of said tube serve to tune said inductance to the output frequency of said oscillator.

16. An electric generating system which includes a vacuum tube having input and output terminals, input and output circuits connected to said input and output a tunable oscillation circuit coupled to the output circuit of said tube and coupled to the iii-'- put circuit thereof, and a fixed impedance common to said output circuit and said oscillation circuit, whereby the reactance of said circuit,- upon the output circuit will increase with a decrease in the frequency circuit is tuned. L

,17. An electric generating system whi h includes a vacuum tube having terminals, input and output circuits connected to said input and output-terminals, respectively, a tunable oscillation circuit tunable to a desired coupled to the input terminals, respectively,

to which said oscillation input and. output 196 and output circuits of said tube, and afixed. im- ,19:

e common to said output circuit andsaid osciu on circuit, whereby the effective coupling between said oscillation circuit and said output circuit increases with a decrease in frequency peda to offset the changes caused by the inductive ;11(

couplings as the said 15. An oscillator modulator circuit compris-&cillator circuit is tuned through-a band of freing a vacuum tube having grid, cathode, and anode; an oscillation circuit including in seriesquencies.

- HAROLD A. WHEELER. 

